The present invention relates to an arrangement for determining two or more superimposed film sheets, particularly X-ray film sheets, in their transport path after withdrawal from a film sheet stack. A light source of a light barrier is located at one side and a photoreceiver of the light barrier is located at the other side of the transport path. The photoreceiver is connected with an evaluating circuit which produces a signal corresponding to the presence of two or more superimposed sheets. The invention also relates to a method of determining two or more superimposed sheets.
Arrangements of the above mention general type are known in the art. One such arrangement is disclosed, for example, in the U.S. Pat. No. 3,882,308. In this arrangement, two photoreceivers are located opposite to the light source. A test sheet lies in a path of light of one photoreceiver, whereas the other photoreceiver controls the transport path of processed sheets. Such an arrangement is, however, expensive and brings a danger of false measurements, inasmuch as the density of the test sheet in the event of irradiation with infrared light changes with time. Because of this, the test sheet must be continuously replaced. This replacement must be performed for each individual exchange of the film material. When it is forgotten to replace the test sheet, the false measurement can take place.